Everything snapping to grid after some accident hotkey. Precise changes available only when I'm holding CTRL
Mode: Edit or Object modes

Hotkey: Shift+Tab

Menu: Mesh/Object » Transform » Snap

Once the tool is activated you are ready to drag your element(s) to its(their) destination. Move your mouse pointer to the target where you want to snap to, hold down Ctrl, move your pointer to adjust (especially if your target is an edge or face).

When satisfied with the result, confirm with LMB Template-LMB.png or Enter (as usual, you can cancel everything with a RMB Template-RMB.png click or by hitting Esc).